JP2516184B2 - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine, and more particularly to an air-fuel ratio feedback control method for an internal combustion engine, which is designed to compensate for changes over time in output characteristics of an exhaust gas concentration detector arranged in an exhaust system of the engine. The present invention relates to a fuel ratio feedback control method.

(Technical background and problems thereof) Conventionally, an exhaust concentration (oxygen concentration) detection value by an exhaust concentration detector (for example, an O ₂ sensor) arranged in an exhaust system of an internal combustion engine is compared with a predetermined reference value, and Based on the comparison result, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled so that the maximum conversion efficiency of the three-way catalyst arranged in the exhaust system of the engine is the theoretical mixture ratio at which the exhaust gas is exhausted. An air-fuel ratio feedback control method for an internal combustion engine, which is designed to improve the characteristics and the like, is generally used (for example, JP-A-57-137633).

The O ₂ sensor used for such air-fuel ratio control uses zirconium oxide or the like as a sensor element, and the amount of oxygen ions passing through the interior of the zirconium oxide or the like is determined by the oxygen partial pressure in the atmosphere and the oxygen in the exhaust gas. The oxygen concentration in the exhaust gas is detected based on the change in the output voltage of the O ₂ sensor according to this change by utilizing the change due to the difference with the partial pressure.

However, the output characteristics of the O ₂ sensor having the above-mentioned configuration change over time, and particularly after the vehicle equipped with the sensor has undergone durable running, the output characteristics deteriorate due to durability, and as a result, the same conditions are met. It is known that the control air-fuel ratio shifts to the rich side as compared with the factory shipment, even though the air-fuel ratio feedback control is performed.

If no measures are taken against such changes over time in the characteristics of the O ₂ sensor, there arises a problem that the operating performance, fuel consumption, and exhaust gas characteristics of the engine deteriorate.

(Object of the Invention) The present invention has been made in order to solve the above-described problems, and corrects the air-fuel ratio of the air-fuel mixture supplied to the engine in accordance with the degree of change over time in the characteristics of the O ₂ sensor to obtain a target air-fuel ratio. An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine that can achieve a fuel ratio.

According to the present invention to achieve such an object, the exhaust gas concentration detection value detected by an exhaust gas concentration detector arranged in the exhaust system of an internal combustion engine is compared with a predetermined reference value, When the air-fuel ratio of the air-fuel mixture supplied to the engine is changed from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value, the air-fuel ratio is changed to the first correction value. At least one of proportional control for increasing / decreasing correction, and integral control for increasing / decreasing the air-fuel ratio at predetermined time intervals by a second correction value when the exhaust concentration detection value is on the lean side or the rich side with respect to the predetermined reference value. In an air-fuel ratio feedback control method for an internal combustion engine that feedback-controls to a target air-fuel ratio by one, the exhaust concentration detection value from the rich side maximum value to the predetermined reference value The ratio between the time of 1 and the second time until the exhaust gas concentration detected value reaches the predetermined reference value from the lean side minimum value, and the first correction value and the first correction value and the first correction value are calculated according to the calculated ratio. Two
There is provided an air-fuel ratio feedback control method for an internal combustion engine, characterized in that at least one of the correction values is changed.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the overall configuration of a fuel supply control device for an internal combustion engine to which the method of the present invention is applied. Reference numeral 1 denotes, for example, an internal combustion engine of four cylinders, an intake pipe 2 communicating with the atmosphere side is connected to the engine 1, and a throttle valve is provided in the middle of the intake pipe 2. The throttle valve 3 is connected to a throttle valve opening sensor 4 that detects the valve opening θ _TH and outputs an electrical signal.
The detection signal is sent to an electronic control unit (hereinafter referred to as “ECU”) 5 that controls an engine by executing arithmetic processing for calculating an air-fuel ratio and the like as described below.

A fuel injection valve 6 is provided between the engine 1 and the throttle valve 3. The fuel injection valve 6 is provided for each cylinder of the engine 1, is connected to a fuel pump (not shown), and a valve opening time for injecting fuel is controlled by a drive signal supplied from the ECU 5.

On the other hand, an intake pipe absolute pressure sensor 8 for detecting the absolute pressure P _BA in the intake pipe 2 is connected to the intake pipe 2 downstream of the throttle valve 3 via a pipe 7, and the detection signal thereof is EC.
Sent to U5.

An engine water temperature sensor 9 which is, for example, a thermistor and detects the temperature Tw of the cooling water is provided on the cylinder peripheral wall of the engine 1 which is filled with the cooling water, and the detection signal is sent to the ECU 5.

Engine speed sensor (hereinafter referred to as "Ne sensor") 10
Is mounted around a cam shaft or crank (not shown) of the engine 1, and this Ne sensor 10 is mounted on the crank shaft 18
One pulse signal (TDC signal) is output every 0 ° rotation.
The TDC signal is sent to the ECU 5.

A three-way catalyst 12 is connected to the exhaust pipe 11 of the engine 1, and the three-way catalyst 12 purifies HC, CO, and NOx components in exhaust gas. O ₂ sensor 13 is an exhaust gas concentration sensor in the exhaust pipe 11 on the upstream side of the three-way catalyst 12 is mounted, the O ₂
The sensor 13 detects the oxygen gas concentration in the exhaust gas, and the detection signal ( _VO2 ) is sent to the ECU5.

Further, a vehicle speed sensor 14 that detects a vehicle speed Sp is connected to the ECU 5, and a detection signal from the vehicle speed sensor 14 is sent to the ECU 5.

The ECU 5 inputs the detection signals from the above-mentioned various sensors and calculates the fuel injection time _TouT of the fuel injection valve 6 by the following equation.

T _ouT = Ti × K ₁ × K _O2 + K ₂ (1) Here, Ti represents the basic fuel injection time of the fuel injection valve 6, and this basic injection time is, for example, the intake pipe absolute pressure P _BA and the engine speed Ne. And is read from the memory device in the ECU 5 based on K _O2 is the O ₂ feedback correction factor,
It is calculated based on the O ₂ feedback correction coefficient calculation subroutine described later. K ₁ and K ₂ are a correction coefficient and a correction variable that are calculated according to the various engine parameter signals, respectively, and fuel efficiency characteristics, engine acceleration characteristics, etc. according to the engine operating state based on the detection signals from the various sensors described above. The predetermined values are determined so as to optimize the various characteristics of.

The ECU 5 outputs a drive signal for opening the fuel injection valve 6 based on the fuel injection time _TouT obtained as described above.

FIG. 2 is a diagram showing a circuit configuration inside the ECU 5 of FIG.
The TDC signal from the Ne sensor 10 is waveform-shaped by the waveform shaping circuit 501 and then supplied to the central processing unit (hereinafter referred to as “CPU”) 503, and at the same time, an engine speed measurement counter (hereinafter referred to as “Me counter”). ) 502 is also supplied. The Me counter 502 counts the time interval from the input of the previous TDC signal from the Ne sensor 10 to the input of the current TDC signal, and the count value Me is proportional to the reciprocal of the engine speed Ne. The Me counter 502 supplies this count value Me to the CPU 503 via the data bus 510.

On the other hand, the output signals from the throttle valve opening (θ _TH ) sensor 4, the absolute pressure (P _BA ) sensor 8, the engine water temperature (Tw) sensor 9, the O ₂ sensor 13, and the vehicle speed (Sp) sensor 14 are respectively The signal is applied to the level correction circuit 504, is corrected to a predetermined voltage level in the circuit 504, and is then sequentially supplied to an analog-digital converter (A / D converter) 506 by a multiplexer 505 which operates based on a command from the CPU 503. The converter 506 converts the output signal of each sensor described above into a digital signal and outputs the digital signal to the CPU 50 via the data bus 510.
Supply to 3.

The CPU 503 further includes a read-only memory (hereinafter referred to as “ROM”) 507, a random access memory (hereinafter referred to as “RAM”) 508, and a drive circuit 509 via a data bus 510.
It is connected to the. ROM507 is details various control programs and correction factor executed by the CPU503 to be described later, and stores various data and Ne-P _R table such as correcting variable. Also,
The RAM 508 temporarily stores calculation results and the like obtained by the CPU 503 executing the various control programs.

Then, the CPU 503 reads out or calculates the coefficient value or the variable value corresponding to the output signal of each sensor from the ROM 507 according to the control program stored in the ROM 507, or calculates and calculates the fuel injection valve 6 based on the calculation formula (1). Fuel injection time T
_ouT is calculated, and the value obtained by this calculation is supplied to the drive circuit 509 via the data bus 510. The drive circuit 509 _{opens the} fuel injection valve 6 for the produced fuel injection time _TouT .

Next, the characteristics of the O ₂ sensor according to the present invention
A method of calculating the O ₂ feedback correction coefficient K _O2 will be described.

As described above, the output characteristic of the O ₂ sensor is deteriorated due to the durable running of the vehicle and the like, and as a result, the feedback-controlled air-fuel ratio is biased to the rich side or the lean side. The degree of deterioration of the O ₂ sensor is the time T _RV (the third value) required to shift from the rich side peak value (maximum value) of the output voltage value (Fig. 3) in a stable engine running state to the predetermined reference value V _REF . Figure t ₂ -t
₃ ) and the lean side peak side (minimum value) to the reference value V
It can be estimated by the value KOX (= T _LV / T _RV ) that represents the ratio to the time T _LV required for the transition to _REF (between t _{6 and} t _{7 in} Fig. 3). It has been experimentally confirmed that this KOX value decreases according to the cumulative distance traveled by the vehicle, that is, the degree of deterioration in durability.

Therefore, in the present invention, the air-fuel ratio is changed to the target air-fuel ratio by changing the proportional control correction value or the integral control correction value to be added to or subtracted from the correction coefficient K _O2 in the feedback control of the air-fuel ratio which will be described later. It is precisely controlled.

This embodiment is applied to the case where the proportional control correction value P _R added to the correction coefficient K _O2 is changed according to the KOX value, and specifically, the value of KOX is set to a plurality of predetermined values KOX _{1 to} KOX ₄ ( KOX ₁ ＞ KOX ₂ ＞ K
OX ₃ > KOX ₄ ) and the proportional control correction value P _{R is changed} by the correction values ΔP _R1 and ΔP _R2 (FIG. 4) as follows.

(1) When KOX> KOX ₁ It is estimated that the air-fuel ratio is largely biased to the lean side, and the correction value ΔP _R2 is added to the correction value P _R.

(2) When KOX ₁ >KOX> KOX ₂ It is estimated that the air-fuel ratio is slightly deviated to the lean side, and the correction value ΔP _R1 (<ΔP _R2 ) is added to the correction value P _R.

(3) When KOX ₂ >KOX> KOX ₃ It is estimated that the air-fuel ratio is controlled to be substantially equal to the target (theoretical) air-fuel ratio, and the correction value P _R is held.

(4) When KOX ₃ >KOX> KOX ₄ It is estimated that the air-fuel ratio is slightly deviated to the rich side, and the correction value ΔP _R1 is subtracted from the correction value P _R.

(5) When KOX> KOX ₄ , it is estimated that the air-fuel ratio is largely deviated to the rich side, and the correction value ΔP _R2 is subtracted from the correction value P _R.

5 and 6 show the rich side proportional control correction value described above.
9 is a program flowchart of a P _R value determination subroutine for changing P _R.

First, in steps 30 to 36, the engine detects the O ₂ sensor.
It is determined whether or not the output voltage V _{O2 of} 13 is in a predetermined operating state that should be reversed in a normal cycle.

That is, in step 30, it is determined whether or not the temperature of the O ₂ sensor 13 is sufficiently high, based on whether or not the engine water temperature Tw is higher than a predetermined value T _WOX , and then in step 31, it is determined whether or not the engine is actually in feedback control. Determine whether. Further, in steps 32 to 35, it is determined whether the engine speed Ne is a value between predetermined values N _eoxL and N _eoxH as a condition of the predetermined operation state (step 32), and the intake pipe absolute pressure is determined.
It is determined whether P _BA is a value between a predetermined value P _BoxL and P _BoxH (step 33), the vehicle speed indicating the cruising state of the vehicle.
It is determined whether Sp is a value between a predetermined value S _poxL and S _poxH (step 34), and the absolute value of the absolute pressure change degree ΔP _BA indicating a stable cruising state is determined by a predetermined width ΔP _BoxA . The determination as to whether it is small (step 35) is executed. Further, in step 36, after these operating conditions are satisfied (after all the determination results of steps 32 to 35 are affirmative (Yes)), it is determined whether or not this operating state is continued for a certain time Tx. It

Therefore, when all the determination results of steps 30 to 36 described above are affirmative (Yes) (operating state shown in FIG. 7), it is determined that the engine is in the predetermined operating state, and the program after step 38 is executed for the first time. To be executed.

If any one of the determination results of steps 30 to 36 is negative (No), the process proceeds to step 37, the averaging count value n _AV described later is set to 0, and the output comparison value V _o2p described later is set to a predetermined reference value V. Set each to _REF and exit this program.

Deterioration of the step 38 to the O ₂ sensor 13 described above in step 58 the degree _{KOX (= T LV / T RV} ) T LV time average T _LVAV for determining, in and T _RV time average T _RVAV is calculated It

Below, the average value from step 38 to step 58
A method of calculating T _LVAV and T _RVAV will be described based on the timing chart of the output voltage value V _O2 of the O ₂ sensor shown in FIG.

Now, suppose that the determination result of the step 36 becomes affirmative (Yes) for the first time at time t _{1 in} FIG.

First, in step 38, the output voltage value of the O ₂ sensor 13 this time.
It is determined whether V _o2n is larger than the predetermined reference value V _REF .
The result of this determination is affirmative (Yes) at time t _{1 in} FIG.
In step 39, it is determined whether or not the previous output voltage value V _o2n-1 is larger than the predetermined reference value V _REF . At t ₁ , this determination result is affirmative (Yes), and the routine proceeds to step 40.

In step 40, the output voltage value V _o2n this time is the output comparison value V
_It is determined whether or not it is greater than _o2p , and in this loop, this output comparison value V _o2p is the predetermined reference value V
Since it is set to _REF , the determination result is affirmative (Yes), and the routine proceeds to step 41. In step 41, the count value of the t _0x timer at this point is reset to O and the count is started again. In the next step 42, the output comparison value V _o2p is set to the current output voltage value V _o2n and Exit the program and go to the next loop.

The output comparison value V _o2p is always rewritten to the output voltage value V _o2n of the O ₂ sensor in the immediately preceding loop between the time points t ₁ and t _{2 in} FIG. 3, but even in this case, the determination result of step 40 is always affirmative. (Yes), and steps 41 and 42 are repeatedly executed.

After the output voltage value V _o2 of the O ₂ sensor 13 reaches the maximum value,
When it begins to fall toward the predetermined reference value V _REF (time t _{2 in} FIG. 3), the determination result of step 40 becomes negative (No),
Steps 41 and 42 are skipped and this program ends.

Therefore, the output voltage value V _o2 of the O ₂ sensor 13 is
The count value of the t _0x timer does not reset until it becomes less than or equal to _REF, and indicates the time elapsed from the time point t ₂ .

When the output voltage value V _o2 of the O ₂ sensor 13 falls below the predetermined reference value V _REF for the first time in this loop (at time t3 in FIG. ₃ ), the determination result of the step 38 becomes negative (No), and the next step 43 Proceed to.

In step 43, it is judged whether or not the output voltage value V _o2n-1 in the previous loop is larger than the predetermined reference value V _REF , and the judgment result becomes affirmative (Yes) at the time point t ₃ , and this time point is judged at the next step 44. T _0x timer count value at t _0x (t _{2 −} t ₃ hours)
_Is set as the transition time T _0x, and the process proceeds to the next step 45. In step 45, it is determined whether or not the transition time T _0x set in step 44 is within the allowable range T _{0xL to} T _0xH . If the determination result is negative (No), skip steps 46 to 48 described later. And proceed to step 49. By performing determination in step 45, eliminating the significantly longer transition time that occurs during the transient period of the engine operating condition and, significantly shorter transition time due to noise generated as shown between t ₇ -t ₈ point of FIG. 3 Can be done.

If the determination result in step 45 is affirmative (Yes), the process proceeds to step 46, and the correction coefficient is _added to the transition time T _0x thus set.
Multiply K _NET and K _PBT to _obtain a new transition time T _0xc . The correction coefficients K _NET and K _PBT are values read from the K _NET- Ne table and the K _PBT- P _BA table shown in FIGS. 8 and 9 according to the engine speed Ne and the intake pipe absolute pressure P _BA , respectively. .
In this way, in step 45, the correction time K 0 _NET , K _PBT is used to correct the transition time T _0x , because the reversal period of the O ₂ sensor is greatly changed according to changes in the engine speed Ne and the intake pipe absolute pressure P _BA. Because it changes to.

The transition time T _0xc corrected in step 46 is _calculated in the next step.
At 47, the value is substituted into the following equation (2), and as a result, the rich side transition time average value T _RVAVn of the voltage value V _o2 from the rich side maximum value to the predetermined reference value V _REF is calculated.

Here, T _RVAVn-1 is the previous value of the rich side transition time average value, COX is an averaging constant for calculating the average value, and the O ₂ sensor of steps 63, 65, 67, ₆₉ , ₇₁ to be described later. Value according to the degree of deterioration COX _{0 to} COX ₄ (however, O <COX _{0 to} COX ₄ <25
Set to 6).

Returning to FIG. 5, in the next step 48, 1 is added to the averaging number count value n _Av representing the number of times the transition times are averaged based on the above equation (2), and in step 49, the output comparison value V _{o2p Is} reset to a predetermined reference value V _REF , the count value of the t _0x timer is reset and started, and the process proceeds to the next step 50.

In step 50, the averaging count value n _Av indicates whether or not the averaging of the transition times in step 47 and step 57 described later has been performed a predetermined number N _Av.
It is determined by whether it is _Av or higher. In addition, the predetermined number N
_Av is step 6 to be described later depending on the degree of deterioration of the O ₂ sensor.
It is set to the required value at 3,65,67,69,71.

If the determination result of step 50 is affirmative (Yes),
The program (FIG. 6) after step 59 described later is executed, and when the result is negative (No), this program is terminated.

As described above Fig. 3 t ₂ ~t ₃ transition time between time T _0x
(= T _RV ) is set, and the rich side transition time average value T _RVAVn is calculated based on the transition time T _0x .

After the output voltage value V _o2 of the O ₂ sensor 13 falls below the predetermined reference value V _REF (after time t ₃ ), the determination results of steps 38 and 43 are both negative, and the process proceeds to the next step 51 and the current loop It is determined whether or not the output voltage value V _{o2n of} is less than or equal to the output comparison value V _o2p . In this case, _since the value of V _o2p is set to the predetermined reference value V _REF in step 49 of the previous loop (time t ₃ ), the determination result is affirmative (Yes) and step 52
Then, the count value of the t _0x timer is reset and started again, and in the following step 53, the output comparison value V _o2p is set to the output voltage value V _o2n in this loop, and this program ends and the next loop is _executed. Move.

Between t ₃ and t _{4 in} FIG. ₃ , the output comparison value V _o2p is always rewritten to the output voltage value V _o2n of the O ₂ sensor in the immediately preceding loop, but even in this case, the determination result of step 51 is always positive ( Yes), and steps 52 and 53 are repeatedly executed.

When the output voltage value V _o2 of the O ₂ sensor 13 once reaches the minimum value at time t _{4 in} FIG. 3 and then starts to rise toward the predetermined reference value V _REF , the determination result of step 51 is negative (No. ), The steps 52 and 53 are skipped and the program ends. At this time, the count value of the t _0x timer is not reset and continues counting from the time point t ₄ .

If the output voltage value V _o2 of the O ₂ sensor 13 drops again before reaching the predetermined reference value V _REF (at time t ₅ ), the determination result of step 51 becomes fixed again (Yes), and the count value of the t _0x timer becomes It is reset and started again (step 52). Therefore, even if the output voltage V _o2 of the O ₂ sensor 13 temporarily changes to the minimum value (or maximum value) and then changes toward the predetermined reference value V _REF , the change direction is reversed before the output voltage V _o2 crosses the reference value V _REF. Then, (t ₅ and t _{9 in} FIG. 3), the t _0x timer is reset, so that it is possible to avoid setting the transition time T _0x by mistake.

When the output voltage value V _o2 of the O ₂ sensor 13 reaches the minimum value again (t
₆ ), the determination result of step 51 is negative (No), t
Elapsed time from t ₆ time by _0x timer is counted.

When the output voltage V _o2 of the O ₂ sensor 13 is increased across the predetermined reference value V _REF (FIG. 3 t ₇ after the time), the determination result in the step 38 is affirmative (Yes), and the then the question of the step 39 ( No) and proceed to step 54.

In step 54, the count value t _0x (t ₆ −t ₇ hours) of the t _0x timer at this point (t ₇ point) is changed to the transition time T _0x (=
T _LV ), proceed to the next Step 55, and proceed to Step 4 above.
Similar to 5, it is determined whether the transition time T _0x is within the allowable range T _{0xL to} T _0xH . In step 56, the transition time T _{0x is set} to the engine speed Ne, the intake pipe absolute pressure P _BA as in step 46.
Corrected with correction factors K _NET and K _PBT according to
T _0xc .

Further, in step 57, the corrected transition time T _0xc is substituted into the following equation (3), and the lean side minimum value is changed to the predetermined reference value V _REF.
Output voltage value V _{o2 to} the lean side transition time average value T _LVAVn
Is calculated.

Here, T _LVAVn-1 is the previous value of the lean side transition time average value, and COX is the same averaging constant as the above equation (2).

At step 58, 1 is added to the averaged number count value n _Av as at step 48, and the routine proceeds to steps 49 and 50 described above.

In this way, the averaging count value n _Av is the predetermined number N
Until the _av, perform repeated calculation of the rich side and the lean side shift time average value of the step 38 to 58, a value representing the degree of deterioration of the O ₂ sensor KOX (= T _LVAV / T
_This is to obtain _RVAV ) more accurately.

When the average value of each transition time to the rich side and the lean side is calculated a predetermined number of times N _Av, and the determination result of step 50 becomes affirmative (Yes), the O ₂ sensor 13 in steps 59 to 77 of FIG. The rich side proportional control correction value P _R is corrected according to the degree of deterioration.

In the determination in steps 59 to 62, the value KOX (= T _LVAV / T _RVAV ) representing the degree of deterioration of the O ₂ sensor and the above-mentioned predetermined values KOX ₁ , K
Compare OX ₂ , KOX ₃ and KOX ₄ respectively (KOX ₁ > KOX ₂ > KOX ₃
> KOX ₄ ). That is, in step 59, the value obtained by multiplying the rich side transition time average value T _RVAV after the predetermined number of times of averaging by a predetermined value KOX ₁ is the lean side transition time average value T after the predetermined number of times of averaging.
_In step 60, the average value T
The value obtained by multiplying a predetermined value KOX ₂ is whether the average value T _LVAV greater than are respectively discriminated _RVAV. On the other hand, in step 61, the value obtained by multiplying the average value T _RVAV by a predetermined value KOX ₄ is the average value T
_In step 62, it is determined whether the average value T is smaller than _LVAV.
The value obtained by multiplying a predetermined value KOX ₃ is whether the average value T _LVAV is smaller than are respectively discriminated _RVAV.

Therefore, the determination result of steps 59 to 62 is completely positive (Ye
s), the value KOX that represents the degree of deterioration is the specified value KOX ₂ and KO
It is a value between X ₃ and in this case, it is estimated that the air-fuel ratio is controlled to be substantially equal to the target air-fuel ratio, and the process proceeds to step 63 and the average used in the above-mentioned equations (2) and (3). Chemical constant
COX and the prescribed number of times of averaging N _Av described above are standard values COX ₀ ,
N Set to _Av0 .

On the other hand, if the determination result in step 59 is negative (No),
Since the KOX value is larger than the predetermined value KOX _1, it is estimated that the air-fuel ratio is largely biased to the lean side, and in step 64, the correction value ΔP _R2 is added to the previous value P _Rn of the rich side proportional control correction value. The value P _Rn is set this time, and in the next step 65, the averaging constant COX
And the predetermined number of times N _Av is COX ₁ (> COX ₀ ), N _Av1 (<N
_Av0 ).

If the determination result in step 60 is negative (No), the KOX value is between the predetermined values KOX ₁ and KOX ₂ , so it is estimated that the air-fuel ratio is slightly deviated to the lean side, and step 66 in the immediately preceding value of the rich side proportional control compensation value P _Rn corrected value [Delta] P _R1 (<
ΔP _R2 ) is added to obtain the current value P _Rn, and in the next step 67, the averaging constant COX and the predetermined number of times N _Av are respectively COX ₂ (COX ₀
Set to _{<COX 2 <COX 1),} N Av2 (N Av0> N Av2> N Av1).

If the determination result in step 61 is negative (No), the KOX value is smaller than the predetermined value KOX ₄ , so it is estimated that the air-fuel ratio is largely deviated to the rich side, and the rich side proportional control is performed in step 68. The correction value ΔP _R2 is subtracted from the previous correction value P _Rn to obtain the current value P _Rn, and in the next step 69, the averaging constant COX
And the predetermined number of times N _Av is COX ₄ (= COX ₁ ), N _Av4 (= N
_Av1 ).

If the determination result in step 62 is negative (No), the KOX value is between the predetermined values KOX ₃ and KOX ₄ , so it is estimated that the air-fuel ratio is slightly biased to the rich side, and step 70 Then, the correction value ΔP _R1 is subtracted from the previous value P _Rn of the rich side proportional control correction value to obtain the current value P _Rn, and in the next step 71, the averaging constant COX and the predetermined number of times N _Av are respectively COX ₃ (= COX ₂ ), N
Set to _Av3 (= N _Av2).

As described above, depending on the degree of deterioration KOX of the O ₂ sensor 13, that is, when the air-fuel ratio is largely biased to the rich side or the lean side, the averaging constant COX becomes a larger value (COX ₁ , COX ₄ ).
To, averaging a predetermined number N _Av smaller value (N _Av1, N _Av4)
By setting the transition time average value T _RVAVn , T
_The degree of averaging of _LVAVn can be accelerated, and thus the air-fuel ratio can be controlled to the target air-fuel ratio swiftly.

In the steps 64, 66, 68, 70, the correction value ΔP _R1 or Δ
This time P of the rich side proportional control correction value corrected by P _R2
In step 72, it is determined whether or not _Rn is larger than the upper limit value P _{RH and} is smaller than the lower limit value P _{RL in} step 73. If the determination results in steps 72 and 73 are both negative (No), ,
Set the corrected correction value P _R1 to the current value P _Rn (step 74),
If either of the determination results is affirmative (Yes), the corrected correction value P _R1 is set to the previous value P _Rn-1 (step 5).

In step 76, the correction value P _R1 thus set is set to R in FIG.
It is stored in the AM 508, and then, in step 77, the averaging number count value n _Av is set to O, and this program ends.

The correction value P _R1 thus stored in the RAM 508 is O
₂ Used in the feedback correction coefficient calculation subroutine, which allows the value of the correction coefficient _Ko2 to be biased toward the rich side or the lean side.

FIG. 10 is a program flowchart of an O ₂ feedback correction coefficient calculation subroutine using the rich side proportional control correction value P _R corrected by the above method.

First, it is determined whether or not the activation of the O ₂ sensor 13 is completed (step 81). That, O ₂ whose output voltage is activated starting point of the O ₂ sensor 13 by the internal resistance detecting method of the sensor 13
Detecting whether Vx (for example, 0.6v) is reached or not, it is determined that it is activated when Vx is reached. If this determination result is negative (No), the correction coefficient K _o2 is set to 1 (step 82). On the other hand, if the determination result is affirmative (Yes), it is determined whether the engine is in the open control region (step 83). This open control includes a high load operation region, a low rotation region, an idle region, a high rotation region, a mixture lean region, etc., and in the high load operation region, for example, the fuel injection time _TouT is larger than a predetermined value Twot. This is the area set to. Here, Twoy is a constant and is the lower limit value of the fuel supply amount required for enriching the air-fuel mixture during high load operation such as when the throttle valve is fully opened. The low rotation speed region is a region where the engine speed Ne is equal to or lower than a predetermined value N _Lop (eg 700 rpm) and the intake pipe absolute pressure P _BA is equal to or higher than a predetermined value P _BIDL (eg 360 mmHg). In the idle region, the engine speed Ne is the predetermined speed N
_It is lower than _HOP (for example, 1000 rpm) and the absolute pressure P _BA is lower than the predetermined pressure P _BIDL .
The engine speed Ne is the predetermined speed N _HOP (eg 3000 rpm)
Is a larger area. The lean air-fuel mixture region is a region where the intake pipe absolute pressure P _BA is smaller than the determination value P _BLS which is set to a larger value as the engine speed Ne increases. When the engine is in any one of the above regions, it is determined that the engine is operating in the open control region, and in this case, the process proceeds to step 82 and K _o2 is set to 1.

On the other hand, if the determination result in step 83 is negative (No), the engine determines that the feedback control is in the operating region and shifts to the closed loop control, and the output level of the O ₂ sensor 13 is the same as when the TDC signal was input last time. Then, it is determined whether or not it is reversed between this input and this input (step 84), and the determination result is affirmative (Ye
If it is s), proportional (P term) control is performed (step 85).
After that, if negative (No), integral control is performed (step 90 and after).

In step 85, it is determined whether or not the output level of the O ₂ sensor 13 is a low level, and if the determination result is affirmative (Yes), the proportional control correction value P _R is set to the rich value corrected by the P _R value determination subroutine described above. the said the side proportional control compensation value P _R1 Ne-P _R table to determine a value corresponding to the engine speed Ne (step 86). Then, in step 87, this correction value
Add P _R to the previous value of the correction coefficient K _o2 . If the determination result of step 85 is negative (No), the lean side proportional control correction value
P _L is read from the Ne-P _L table (step 88), and the read correction value P _L is subtracted from the previous value of the correction coefficient K _o2 (step 89).

When the determination result of step 84 is negative (No), integration control is performed as follows. First, in step 90,
Similar to step 85, it is determined whether the output level of the O ₂ sensor 13 is low. If the determination result is affirmative (Yes), 1 is added to the count value N _IL of the TDC signal pulse (step 91), and whether or not the count number N _IL has reached a predetermined value N _I (for example, 4). Is determined (step 92). As a result of this determination, if the count number N _IL has not reached N _I yet, the correction coefficient K _o2 is held at the value at the previous loop (step 93), and when the count number N _IL reaches N _I Is the correction factor K
A correction value Δk corresponding to the engine speed Ne is added to _o2 (step 94), and the number of pulses N _IL counted up to that time is N _IL.
Is reset to 0 (step 95), and the correction value Δk is added to the correction coefficient K _o2 every time N _IL reaches N _I. On the other hand, if the determination result in step 90 is negative (No), 1 is added to the count number N _IH of the TDC signal pulse (step 96), and the count number N _IH reaches the predetermined value N _I. It is determined whether or not (step 97) and the determination result is negative (N
In the case of o), the value of the correction coefficient K _o2 is held at the value at the previous loop (step 98), and when the determination result is affirmative (Yes), the correction value Δk is subtracted from the correction coefficient K _o2 (step 98). 9
9) The counted pulse number N _IH is reset to 0 (step 100), and the correction value Δk is subtracted from the correction coefficient K _o2 each time N _IH reaches N _I , as described above.

By correct the rich side proportional control compensation value P _R, applying the correction value P _R was modified thus the calculation of O ₂ feedback correction coefficient K _o2 in accordance with the deterioration degree of the thus O ₂ sensor 13, O ₂ When the air-fuel ratio is biased to the rich side due to deterioration of the sensor 13, the value of the correction coefficient K _o2 is made small, while when it is biased to the lean side, the value of the correction coefficient K _o2 is made large to set the target air-fuel ratio. It can be matched to the air-fuel ratio.

In the present embodiment, the rich side proportional control correction value P _R is corrected according to the degree of deterioration of the O ₂ sensor 13, but the present invention is not limited to this, and the lean side proportional control correction value, rich side and lean side integral control is performed. The same effect can be obtained by correcting at least one of the correction values.

(Effect of the Invention) As described in detail above, according to the present invention, the exhaust gas concentration detection value detected by the exhaust gas concentration detector arranged in the exhaust system of the internal combustion engine is compared with a predetermined reference value, and the result is supplied to the engine. The air-fuel ratio of the air-fuel mixture is increased or decreased by the first correction value when the exhaust concentration detection value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value. When the exhaust gas concentration detection value is on the lean side or the rich side with respect to the predetermined reference value, at least one of the proportional control and the integral control for increasing / decreasing the air-fuel ratio every predetermined time by the second correction value In an air-fuel ratio feedback control method for an internal combustion engine, which performs feedback control to an air-fuel ratio, a first method from when the exhaust concentration detection value reaches a predetermined reference value from a rich side maximum value
And the second time until the exhaust gas concentration detected value reaches the predetermined reference value from the lean side minimum value,
Since at least one of the first correction value and the second correction value is changed according to the ratio thus obtained, even if the characteristics of the exhaust gas concentration detector change over time, the mixture The target air-fuel ratio can be achieved by correcting the air-fuel ratio of the engine, and thus the engine operating performance, fuel consumption, and exhaust gas characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an air-fuel ratio control apparatus for carrying out the method of the present invention, FIG. 2 is a block diagram showing the internal configuration of the electronic control unit of FIG. 1, and FIG. 3 is of FIG. O ₂ a timing chart showing the time change of the output voltage value V _o2 of the sensor 13, the fourth graph figure showing the relationship between the correction value [Delta] P _R value KOX representing the deterioration degree of the O ₂ sensor 13, FIG. 5 and the FIG. 6 is a program flow chart of the P _R value determination subroutine according to the present invention, FIG. 7 is a graph showing an engine operating region for executing the program flow charts shown in FIGS. 5 and 6, and FIG. 8 is a correction coefficient K _NET. 9 is a graph showing the relationship between the engine speed Ne and the engine speed Ne, FIG. 9 is a graph showing the relationship between the correction coefficient K _PBT and the intake pipe absolute pressure P _BA, and FIG. 10 is O ₂
7 is a program flowchart of a feedback correction coefficient K _o2 calculation subroutine. 1 ... internal combustion engine, 5 ... electronic control unit (ECU), 8 ... intake pipe absolute pressure ( _PBA ) sensor, 10 ...
Engine speed (Ne) sensor, 13 …… O ₂ sensor.

Claims (1)

(57) [Claims] 1. An exhaust gas concentration detection value detected by an exhaust gas concentration detector arranged in an exhaust system of an internal combustion engine is compared with a predetermined reference value to detect an air-fuel ratio of an air-fuel mixture supplied to the engine. When the value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value,
When the exhaust gas concentration detection value is on the lean side or the rich side with respect to the predetermined reference value, the proportional control is performed to increase / decrease the air-fuel ratio by the first correction value, and the air-fuel ratio is changed by the second correction value at predetermined time intervals. In an air-fuel ratio feedback control method for an internal combustion engine that feedback-controls to a target air-fuel ratio by at least one of integration control for increasing / decreasing, the exhaust concentration detected value from a rich side maximum value to the predetermined reference value The ratio between the time of 1 and the second time until the exhaust gas concentration detected value reaches the predetermined reference value from the lean side minimum value, and the first correction value and the first correction value and the first correction value are calculated according to the calculated ratio. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that at least one of the correction values of 2 is changed.